1. Field of the Invention
The present invention relates to receptor sheets for use in transfer or deposit imaging systems and particularly to receptor sheets having indicia on a nonimage receiving surface.
2. Background of the Art
Many imaging materials and processes require specialty papers in order to perform at their highest levels. Photographic paper often comprises a white paper base with a coating of resin or pigmented resin. Usually the pigment is white (e.g., TiO.sub.2) in order to provide a bright white background (U.S. Pat. No. 4,481,289, 4,447,524, and 4,312,937). Transfer or deposit imaging systems such as thermal transfer (e.g., U.S. Pat. No. 4,690,858 and 4,614,682), photoresist transfer (e.g., U.S. Pat. No. 4,710,445, 4,656,114, and 4,666,817), ink jet printing, and the like perform best when a surface has been particularly designed to function in combination with the imaging material being deposited. Sometimes the design is enhanced to contribute to either the optical qualities of the material or to its physical adherence properties.
For example, U.S. Pat. No. 4,614,682 describes a paper receiving sheet for thermal image transferring processes as plain paper, or paper with a coating of resin and filler (e.g., pigments such as titanium oxide, or zinc oxide) for facilitating the transfer of a dye component from the donor layer to the transfer sheet. U.S. Pat. No. 4,690,858 describes the use of coated paper as a receptor sheet (col. 4, lines 31-34).
These receptor sheets do not necessarily have the same type of surfaces on both sides of the base layer. This can be done to save costs during manufacture or to prevent images from being deposited on both sides of the receptor With many types of differences between the surfaces of the receptor sheet, it is still somewhat difficult to distinguish the receptor surface from the backside. This can create an appearance of poor performance in the product if the wrong surface is used. To assist in the proper recognition of the receptor surface, the backside of the receptor sheet is sometimes printed with ink as with a logo of the manufacturer, to distinguish the front side from the back. Dark inks can often be seen through the sheet, and even the low optical density printing used can be observed with transmitted lighting. The printing step may also require a separate processing line, which adds to the expense, and certain preferred coatings (e.g., olefins and polyester) do not accept print easily.
Polyolefin film filled with titania and having a backside adhesive coating are used as diaper tabs. The film is sometimes marked by embossing after extrusion. The embossing creates significant variations in the transmission optical density as well as the reflection optical density of the film. The embossing affects both surfaces of the film, but is partially masked on one side by the adhesive.